Data Validation drop-down based on the result of previous cell

I need to create a data validation drop-down field based upon the result of the previous field. For example, A1 has a drop-down list to select Home Loan, Personal Loan or Overdraft. I need B1 to have a drop down field based upon the result in A1 (if A1 is Home Loan, then I need to specify a selection of loan purposes specific to home loans, the same for personal loans and overdrafts). This will need to continue through the worksheet in Columns A and B.

Any help is greatly appreciated.
Cheers
Stuart